Step 1: Divide the number into separate digits:
7930 => 7 9 3 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 9 = 2
9 to 3 = 6
3 to 0 = 3
0 to 7 = 7
Step 3: Combine the filters to a string:
2 6 3 7 = 2637